Method and apparatus for operating a gas turbine with silane oil as fuel

ABSTRACT

The invention relates to a method of driving a shaft by reaction of silanes, preferably silane oils, with air in a double combustion chamber and an assiciated drive mechanism. The hydrogen of the silanes reacts in the first combustion chamber with an insufficient level of oxygen of the air supplied, thereby producing high temperatures. At said high temperatures, the nitrogen from the air supplied reacts with the silicon of the silane to form silicon nitride. The resultant combustion gases and dust and the non-combusted hydrogen are mixed in the second combustion chamber with a large quantity of cold compressed air, the hydrogen undergoing late burning, and they subsequently enter a turbine chamber to actuate turbine blades connected to a shaft. The method is particularly environmentally-friendly since no toxic or polluting waste gases are produced.

SPECIFICATION CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT/DE 97/00612 filed Mar. 26,1997 and based upon German national application 196 12 507.3 of Mar. 29,1996 under the International Convention.

FIELD OF THE INVENTION

The present invention is directed to a method of driving a shaft as wellas to a drive mechanism for carrying out such method.

BACKGROUND OF THE INVENTION

From DE-OS-22 31 008 it is known to use tetrasilane (Si₄ H₁₀) as arocket propellant. DE 42 15 835 c2 also describes silicon hydrides,preferably silane oils, as rocket propellants. The production of suchsilane oils is described in DE-PS 21 39 155. In the systems described inthese publications the silane oils are burned together with liquidoxygen, liquid chlorine or liquid fluorine.

In the non-published German patent application P 44 37 524.7 (see alsoU.S. Pat. No. 5,730,390 of Mar. 24, 1998) a method for operating areaction-type missile propulsion system and a drive mechanism forcarrying out such method are described. The drive mechanism is operatedin such a manner that silicon hydride compounds are reacted withnitrogen and/or nitrogen compounds at increased temperatures in thepresence of an oxidizing agent for the hydrogen of the silicon hydridecompounds. Preferably, the nitrogen and the oxydizing agent can be takenfrom the atmosphere of the earth so that a corresponding oxidizing agentfor the silicon hydride compounds need not be carried along in themissile. Preferably, silane oils are burned as silicon hydridecompounds.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a method of drivinga shaft as well as a drive mechanism therefor which operate with veryhigh temperatures and a correspondingly high efficiency and which havelittle pollution effects.

SUMMARY OF THE INVENTION

According to the invention this the following steps:

a. introducing silicon hydrides and air into the first part of a doublecombustion chamber;

b. reacting the hydrogen of the silicon hydrides with asub-stoichiometric amount of oxygen of the introduced air for thegeneration of increased temperatures;

c. reacting the excess of the introduced nitrogen of the air at theincreased temperatures with the silicon of the silicon hydrides for thegeneration of silicon nitride;

d. discharging the combustion gases and combustion dusts and thenon-burned hydrogen portion from the first part into the second part ofthe double combustion chamber and mixing these combustion products witha large amount of air with after-burning of the hydrogen; and

e. directing the combustion gases and combustion dusts into a turbinechamber for driving turbine blades connected to a shaft.

The N₂ -molecule as such, notwithstanding its triple bond, is extremelyinactive and tends to open its linkage only with electron bombardment,for instance in thunderstorms, and reacts with oxygen so that nitricoxides are formed. However, above 1400° C. hot nitrogen reacts withfinely distributed silicon and forms silicon nitride Si₃ N₄. The reasonsfor this nitrogen combustion can be found in the fact that silicon, incontrast to carbon, cannot enter into double bonds or triple bonds.Nitrogen shows an especially good reaction performance with siliconhydride compounds. The invention takes advantage of this recognition anduses intentionally nitrogen or nitrogen compounds for the reaction withsilicon hydride compounds whereby an especially efficient propellingsystem can be obtained. Nitrogen is at disposal in big amounts in theatmosphere so that a high efficiency with low costs results.

When burning silicon hydride compounds, especially silane oils, withcompressed air the oxygen portion reacts with the hydrogen of the silanechain in accordance with the equation

    4H+O.sub.2 =2H.sub.2 O.

In this hydrogen-oxygen combustion temperatures of about 3000° C. arereached. This temperature is sufficient in order to crack the N₂-molecule which is presented by the supply of the compressed air.According to the equation

    4N+3Si=Si.sub.3 N.sub.4

the nitrogen radicals now attack the free silicon atoms with extremevehemence. Silicon nitride is formed which has a molecular weight of 140and thus is nearly three times as heavy as carbon dioxide.

Of course, the cited reaction occurs only with correspondingly hightemperatures. In the air silane oils after ignition burn only to developred-brown amorphous silicon monoxide since the combustion substance hasnot enough oxygen on account of the rapidity of the combustion. Noreaction with nitrogen takes place since nitrogen does not form any freeradicals under these conditions.

In other words, at a sufficiently high temperature the silicon hydridecompounds are ultimately thermally decomposed into Si and H. The highlyreactive H-atoms bind the oxygen of the air for the generation of water.The linkage enthalpy of H₂ O becoming free thereby supplies necessaryenergy for achieving high combustion temperatures. The N₂ -dissociationincreases very much above about 2500 K. Since the oxygen is bound inwater the highly reactive atomic nitrogen reacts with Si for thegeneration of Si₃ N₄. During this reaction the very high linkageenthalpy of Si₃ N₄ is liberated. It amounts to -745 kJ/mol at T=298 K.

Since air consists of oxygen for only 20% and since the oxygen/hydrogenreaction is energetically more beneficial than the oxygen/siliconreaction, the ratio between the supply of air and the supply of siliconhydride can be adjusted such that a portion of the hydrogen is notburned while the nitrogen combustion of the silicon takes placequantitatively. In this I prevent the generation of silicon oxidesaltogether. With a conventional jet engine the 80% hydrogen of the airare coaccelerated in a non-burned manner. The same occurs if siliconhydrides are burned with an excess of air. The generated silicon oxideswould prevent confirming of nitrogen. Accordingly, the described methodprovides an air-breathing rocket propulsion unit since no oxygen tankhas to be carried along and the mixture of the oxygen of the air and thenitrogen is 100% burned.

Preferably, as silicon hydride compounds silane oils, especially thosewith a chain length of Si₅ H₁₂ to Si₉ H₂₀, are used. Such silane oilsare described in the already mentioned DE-PS 21 39 155. Surprisingly,such long-chain silanes are not self-inflammable in the air. They havethe constistency of paraffin oils and can be manufactured simply. Theycan be pumped so that they can be supplied to an appropriate combustionchamber without problems.

According to the inventive method water vapor and silicon nitride dustsare generated. Both substances are not toxic and do not represent anenvironmental load. The generated dusts can be collected by filteringthe combustion gases after leaving the turbine chamber while the gasessubstantially consisting of water vapor can be discharged into theatmosphere. Accordingly, the method and the corresponding drivemechanism have very little pollution effects.

Preferably, compressed air is introduced into the combustion chamber forimproving the efficiency. The air is taken from the environment, iscompressed by means of a compressor and is introduced into thecombustion chamber. Preferably, the compressor is driven by the shaft.

Accordingly, air is taken from the atmosphere and is then preferablycompressed. By contact of the air line with the walls of the doublecombustion chamber the same are cooled and thus protected fromvaporization. The air heated to above 1500° C. helps to initiate the N₂-dissociation. Of course, the combustion chamber has to consist ofmetals suitable for this.

In order to save costs with the inventive method but also in order tocompletely exclude the silicon/oxygen combustion it can be advantageousto add powdered silicon or metal silicides, for instance magnesiumsilicide, to the silicon hydrides. It is known that magnesium reactswith nitrogen with the discharge of a large amount of heat.

After the start of the described combustion in the first chamber of thedouble combustion chamber and after the adjustment of the correspondingoperating temperatures the method will run in the described manner, anda part of the non-burned hydrogen together with the hot H₂ O--Si₃ N₄mixture with a temperature between 2500 and 3000° C. will flow into thesecond part of the double combustion chamber (after-burning chamber).These gases are much too hot in order to drive a shaft by means ofturbine blades. Therefore, in the second part of the combustion chamberheat is directly used for compressing cold air.

Cold air compressed by the compressor is introduced into the upper partof the second combustion chamber through controllers. The combustiongases having a temperature of more than 2500° C. are cooled with amultiple amount of air, wherein simultaneously the non-burned hydrogenis after-burned. In this manner large amounts of turbine gasesconvertable into work are generated, which are introduced into a turbinechamber and drive the turbine blades there. As already mentioned, theturbine shaft is connected to the air compressor.

Practically, the outlet of the turbine chamber leads into a filterchamber which has an outlet leading to the atmosphere. In the filterchamber the silicon nitride dusts generated by the reaction are retainedso that substantially only water vapor is discharged into theatmosphere.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described below in detail by means of an example inconnection with the drawing.

The sole FIGURE of the drawing shows a schematic longitudinal sectionthrough a drive mechanism formed according to the invention.

SPECIFIC DESCRIPTION

The drive mechanism consists of a housing including, in the FIGURE fromleft to right, in succesion, a main combustion chamber 1, an afterburnerchamber 2, a turbine chamber 3 and a compressor chamber 4. The housingis restricted between the several chambers so that appropriateconnection channels are formed. Of course, the housing is comprised ofappropriate materials or is provided with suitable linings in order towithstand the increased temperatures (up to 3000° C.), especially thoseoccuring in the main combustion chamber 1, as well as the occuringincreased pressures.

A fuel mixing chamber 7 is located at the left end of the FIGURE. Aconduit 10 for the supply of silane oil and a conduit 11 for the supplyof silicon/metal silicide dust open into the mixing chamber 7.Furthermore, an appropriate mixing device is provided within the mixingchamber 7. A channel extends from the mixing chamber 7 into the maincombustion chamber 1. A plurality of air supply apertures 8 areannularly disposed laterally from the central supply channel for thefuel (silane oil+Si/metal silicide).

These air supply apertures are connected to a supply conduit 12 for hotair annularly surrounding the main combustion chamber 1, the afterburnerchamber 2 and the turbine chamber 3. The supply conduit 12 for hot airis connected to an outlet 17 of the compression chamber 4. Furthermore,the compression chamber 4 has an outlet 18 which is connected to asupply line 9 for cold air which laterally opens into the afterburnerchamber 2. The supply line 9 for cold air extends through a controller13 by means of which the supply of cold air into the afterburner chambercan be regulated.

A shaft 5 is centrally disposed within the turbine chamber 3 and withinthe compressor chamber 4 and extends through both chambers. The shaft 5is rotated by the reactions taking place within the main combustionchamber and the afterburner chamber and can supply, for instance,mechanical energy or electrical energy through a generator. Turbineblades are disposed at the shaft within the turbine chamber 3. Theseturbine blades are driven by the combustion gases or combustion dustsentering into the turbine chamber from the afterburner chamber androtating the shaft 5 hereby. Blades disposed within the compressorchamber 4 compress air entering through inlets 6 by means of therotating shaft 5. The air is introduced into the conduits 9 and 12through the outlets 17 and 18.

The turbine chamber 3 is connected through outlets for the combustiongases or combustion dusts to filter boxes 19 in which replaceable filtersacks 20 are disposed. These filter sacks 20 retain the dusts(substantially silicon nitride) while the combustion gases(substantially water vapor) are discharged to the atmosphere throughoutlets 21.

The above-described drive mechanism operates in the following manner:

Silane oil is pumped into the mixing chamber 7 through the conduit 10.Metal silicide dust is supplied through the conduit 11. These componentsare mixed within the mixing chamber. The generated mixture is introducedinto the main combustion chamber 1 through the correspondingintroduction conduit. The main combustion chamber 1 receives compressedhot air through the introduction apertures 8. The oxygen of the airreacts vehemently with the hydrogen of the silane oil. The nitrogen ofthe air reacts with the silicon of the silane oil and generates siliconnitride by the generated very high temperatures. The generatedcombustion gases or combustion dusts (with an excess of H₂) enter theafterburner chamber 2 into which compressed cold air is introducedthrough the conduit 9. The introduced cold air causes a combustion ofthe excess H₂ to form water vapor. The turbine blades in the turbinechamber 3 are applied with the gases and dusts discharged by theafterburner chamber 2 so that the shaft 5 is rotated. The correspondinggases and dusts leave the turbine chamber through the outlets 16, enterthe filter sacks 20 within the filter chambers 19 in which the dusts arefiltered, and are discharged into the atmosphere through the outlets 21.

I claim:
 1. A method of driving a shaft, said method comprising thefollowing steps:a. introducing silicon hydrides and air into a firstpart of a double combustion chamber; b. reacting the hydrogen of thesilicon hydrides with a sub-stoichiometric amount of oxygen of theintroduced air for the generation of increased temperatures; c. reactingthe introduced nitrogen of the air at the increased temperatures withthe silicon of the silicon hydrides for the generation of siliconnitride; d. discharging combustion gases and combustion dusts and anon-burned hydrogen portion from the first part into a second part ofthe double combustion chamber and mixing them with a large amount of airfor after-burning of the hydrogen; and e. directing the combustion gasesand combustion dusts into a turbine chamber for driving of turbineblades connected to a shaft.
 2. The method according to claim 1 whereincompressed air is introduced into the first and/or second part of thecombustion chamber.
 3. The method according to claim 2, wherein thecompressed air is generated by a compressor which is driven by theshaft.
 4. The method according to claim 1, wherein hot air is introducedinto the combustion chamber.
 5. The method according to claim 4 whereinthe hot air is generated by heat exchange with the wall of thecombustion chamber.
 6. The method according to claim 1, wherein thecombustion gases and combustion dusts discharged from the turbinechamber are filtered.
 7. The method according to claim 1, wherein silaneoils are used as silicon hydride compounds.
 8. The method according toclaim 1 wherein at least one member selected from the group whichconsists of powdered silicon and metal silicides is added to the siliconhydrides.
 9. The method according to claim 1, wherein the supply ofoxygen of the air is regulated in such a manner that no silicon oxidesare generated and thereby a portion of the hydrogen is not burned in thefirst part of the double combustion chamber.
 10. A drive mechanism forcarrying out a method which comprises the following steps:a. introducingsilicon hydrides and air into a first part of a double combustionchamber; b. reacting the hydrogen of the silicon hydrides with asub-stoichiometric amount of oxygen of the introduced air for thegeneration of increased temperatures; c. reacting the introducednitrogen of the air at the increased temperatures with the silicon ofthe silicon hydrides for the generation of silicon nitride; d.discharging combustion gases and combustion dusts and a non-burnedhydrogen portion from the first part into a second part of the doublecombustion chamber and mixing them with a large amount of air forafter-burning of the hydrogen; and e. directing the combustion gases andcombustion dusts into a turbine chamber for driving of turbine bladesconnected to a shaft, the drive mechanism comprising: a combustionchamber; a supply conduit for the silicon hydrides leading into thecombustion chamber; a supply conduit for air leading into the combustionchamber; an afterburner chamber connected to the combustion chamber; asupply conduit for air leading into the afterburner chamber; a turbinechamber; a connection between the afterburner chamber and the turbinechamber for the introduction of the combustion gases and combustiondusts into the turbine chamber; and a drive shaft with turbine bladeswithin the turbine chamber.
 11. The drive mechanism according to claim10, further comprising a compressor for the generation of compressed airfor the combustion chamber and/or the afterburner chamber which isdriven by the drive shaft.
 12. The drive mechanism according to claim10, wherein the supply conduit is in contact with at least one of thewall of the combustion chamber, of the afterburner chamber and/or of theturbine chamber.
 13. The drive mechanism according to claim 10, whereinan outlet of the turbine chamber leads into a filter chamber which hasan outlet leading to the atmosphere.